Double metal cyanide complex catalysts

ABSTRACT

Improved double metal cyanide catalysts are disclosed. The substantially amorphous catalysts of the invention are more active for polymerizing epoxides than conventional DMC catalysts, which have a substantial crystalline component. Polyol products made with the catalysts are unusually clear, have exceptionally low unsaturations, and contain no detectable amount of low molecular weight polyol impurities. A method of making the improved DMC catalysts, which involves intimately combining the reactants, is also disclosed.

This is a division of application Ser. No. 08/156,534, filed Nov. 23,1993 and now U.S. Pat. No. 5,470,813.

FIELD OF THE INVENTION

The invention relates to double metal cyanide (DMC) complex catalystcompositions. The catalysts are highly active in epoxidepolymerizations. The invention includes an improved method for preparingthe compositions. Polyether polyol products made using the catalystcompositions have exceptionally low unsaturations.

BACKGROUND OF THE INVENTION

Double metal cyanide complex compounds are well known catalysts forepoxide polymerization. The catalysts are highly active, and givepolyether polyols that have low unsaturation compared with similarpolyols made using basic (KOH) catalysis. Conventional DMC catalysts areprepared by reacting aqueous solutions of metal salts and metal cyanidesalts to form a precipitate of the DMC compound. The catalysts can beused to make a vadety of polymer products, including polyether,polyester, and polyetherester polyols. Many of the polyols are useful invarious polyurethane coatings, elastomers, sealants, foams, andadhesives.

Conventional DMC catalysts am usually prepared in the presence of a lowmolecular weight complexing agent, typically an ether such as glyme(dimethoxy-ethane) or diglyme. The ether complexes with the DMCcompound, and favorably impacts the activity of the catalyst for epoxidepolymerization. In one conventional preparation, aqueous solutions ofzinc chloride (excess) and potassium hexacyanocobaltate are combined bysimple mixing. The resulting precipitate of zinc hexacyanocobaltate isthen mixed with aqueous glyme. An active catalyst is obtained that hasthe formula:

    Zn.sub.3  Co(CN).sub.6 !.sub.2.xZnCl.sub.2.yH.sub.2 O.zGlyme

Other known complexing agents include alcohols, ketones, esters, amides,ureas, and the like. (See, for example, U.S. Pat. Nos. 3,427,256,3,427,334, 3,278,459, and Japanese Pat. Appl. Kokai Nos. 4-145123,3-281529 and 3-149222). Generally, the catalyst made with glyme has beenthe catalyst of choice. The catalysts have relatively high surfaceareas, typically within the range of about 50-200 m² /g.

Double metal cyanide compounds prepared in the absence of a complexingagent are highly crystalline (as shown by X-ray diffraction analysis),and are inactive for epoxide polymerization. When the complexing agentsdescribed above are used, the resulting catalysts actively polymerizeepoxides. Our X-ray diffraction analyses of active DMC complexesprepared according to methods known in the art suggest that conventionalDMC catalysts are actually mixtures of a highly crystalline DMC compoundand a more amorphous component. Typically, conventional DMCcatalysts--which are generally prepared by simple mixing--contain atleast about 35 wt.% of highly crystalline DMC compound. DMC compoundsuseful as epoxide polymerization catalysts and containing less thanabout 30 wt.% of highly crystalline DMC compound are not known.

Double metal cyanide catalysts generally have good activity for epoxidepolymerizations, often much greater than conventional basic catalysts.However, because the DMC catalysts are rather expensive, catalysts withimproved activity are desirable because reduced catalyst levels could beused.

Double metal cyanide catalysts normally require an "induction" period.In contrast to basic catalysts, DMC catalysts ordinarily will not beginpolymerizing epoxides immediately following exposure of epoxide andstarter polyol to the catalyst. Instead, the catalyst needs to beactivated with a small proportion of epoxide before it becomes safe tobegin continuously adding the remaining epoxide. Induction periods of anhour or more are typical yet costly in terms of increased cycle times ina polyol production facility. Reduction or elimination of the inductionperiod is desirable.

An advantage of DMC catalysts is that they permit the synthesis of highmolecular weight polyether polyols having relatively low unsaturation.The adverse impact of polyol unsaturation on polyurethane properties iswell documented. (See, for example, C. P. Smith et el., J. Elast.Plast., 24 (1992) 306, and R. L. Mascioli, SPI Proceedings, 32nd AnnualPolyurethane Tech./Market. Conf. (1989) 139.) When a DMC catalyst isused, polyols having unsaturations as low as about 0.015 meq/g can bemade. Polyether polyols with even lower unsaturations can be made if asolvent such as tetrahydrofuran is used to make the polyol. However, forcommercial polyol production, the use of a solvent is not particularlydesirable. Thus, other ways to further reduce polyol unsaturation areneeded.

When conventional DMC catalysts are used to polymerize epoxides, thepolyether polyol products contain relatively low levels (about 5-10 wt.%) of low molecular weight polyol impurities. A way to eliminate thesepolyol impurities is desirable because improved polyurethanes couldresult from the use of more monodisperse polyols.

Double metal cyanide complex catalyst residues are often difficult toremove from polyether polyols, and a wide vadety of methods have beendeveloped to cope with the problem. Removal of DMC catalyst residuesfrom the polyols promotes long-term storage stability and consistentpolyol performance in urethane formulation. Most methods involve somekind of chemical treatment of the polyol following polymerization. Therehas been little progress made in developing catalyst preparation methodsthat ultimately facilitate catalyst removal from the polyol products.

SUMMARY OF THE INVENTION

The invention is an improved catalyst for polymerizing epoxides. I havesurprisingly found that substantially amorphous DMC complexes are muchmore active than conventional DMC complexes for epoxide polymerization.In addition, the amorphous complexes are more quickly activated (showreduced induction periods) compared with conventional DMC catalysts.

The catalysts of the invention comprise at least about 70 wt. % of asubstantially amorphous DMC complex; more preferred compositionscomprise from about 90-99 wt. % of the substantially amorphous DMCcomplex.

The invention also includes compositions which comprise thesubstantially amorphous DMC complexes described above, and up to about30 wt. % of a highly crystalline DMC compound; more preferredcompositions contain less than about 1 wt. % of the highly crystallineDMC compound.

The invention includes a method for preparing the improved catalysts.Although conventional methods for making DMC complex catalysts have beenknown for about 30 years, no one has previously appreciated that themethod of combining the reactants is extremely important. I have nowdiscovered, quite surprisingly, that highly active, substantiallyamorphous DMC complexes are produced only when the reactants areintimately combined during catalyst preparation. Aqueous solutions of awater-soluble metal salt and a water-soluble metal cyanide salt areintimately combined in the presence of a complexing agent to produce anaqueous mixture containing the DMC complex catalyst. The catalyst, whichis then isolated and dried, comprises at least about 70 wt. % of asubstantially amorphous DMC complex.

The invention also includes a method for preparing an epoxide polymer.The method comprises polymerizing an epoxide in the presence of acatalyst which comprises at least about 70 wt. % of a substantiallyamorphous DMC complex.

The invention also includes polyether polyol compositions that areuniquely available from using the catalysts of the invention. Thepolyols have exceptionally low unsaturations and contain unusually lowlevels of low molecular weight polyol impurities.

Finally, the invention includes a method for improving the filterabilityof a DMC complex catalyst from a polyether polyol product followingepoxide polymerization. The method comprises using, as a polymerizationcatalyst, a substantially amorphous DMC complex catalyst of theinvention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a plot of propylene oxide consumption versus time during apolymerization reaction with one of the catalyst compositions of theinvention at 250 ppm catalyst. The induction time for the run ismeasured as discussed in Example 6 from the intersection of the extendedbaseline and slope measurements.

DETAILED DESCRIPTION OF THE INVENTION

The catalysts of the invention, unlike conventional DMC compounds knownin the art as useful for epoxide polymerization, comprise at least about70 wt. % of a substantially amorphous DMC complex. More preferredcatalysts of the invention comprise at least about 90 wt. % of asubstantially amorphous DMC complex; most preferred are catalystscomprising at least about 99 wt. % of a substantially amorphous DMCcomplex.

As defined in this application, "substantially amorphous" meanssubstantially noncrystalline, lacking a well-defined crystal structure,or characterized by the substantial absence of sharp lines in the X-raydiffraction pattern of the composition. Powder X-ray diffraction (XRD)patterns of conventional double metal cyanide catalysts showcharacteristic sharp lines that correspond to the presence of asubstantial proportion of a highly crystalline DMC component. Highlycrystalline zinc hexacyanocobaltate prepared in the absence of anorganic complexing agent, which does not actively polymerize epoxides,shows a characteristic XRD fingerprint of sharp lines at d-spacings ofabout 5.07, 3.59, 2.54, and 2.28 angstroms.

When a DMC catalyst is made in the presence of an organic complexingagent according to conventional methods, the XRD pattern shows lines forthe highly crystalline material in addition to broader signals fromrelatively amorphous material, suggesting that conventional DMCepoxidation catalysts are actually mixtures of highly crystalline DMCcompound and a more amorphous component. Typically, conventional DMCcatalysts, which are generally prepared by simple mixing, contain atleast about 35 wt. % of highly crystalline DMC compound.

The catalysts of the invention are distinguishable from conventional DMCcompositions based on their substantial lack of crystalline material.The substantial lack of crystallinity is evidenced by an XRD patternshowing that little or no highly crystalline DMC compound is present.When a zinc hexacyanocobaltate catalyst is prepared according to themethod of the invention using tert-butyl alcohol as a complexing agent,for example, the X-ray diffraction pattern shows essentially no linesfor crystalline zinc hexacyanocobaltate (5.07, 3.59, 2.54, 2.28angstroms), but instead has only two major lines, both relatively broad,at d-spacings of about 4.82 and 3.76 angstroms. Spiking experimentsdemonstrate that DMC catalysts prepared by the method of the inventiontypically contain less than about 1 wt. % of highly crystalline DMCcompound. X-ray results appear in Table 1.

Conventional DMC catalysts typically contain at least about 35 wt. % ofhighly crystalline DMC compound. No one has previously recognized thedesirability of preparing substantially amorphous catalysts, and thepotential value of reducing the content of highly crystalline DMCcompounds in these catalysts. It appears, based on my results, that thehighly crystalline DMC compound acts as either a diluent or as a poisonfor the more active amorphous form of the catalyst, and its presence ispreferably minimized or eliminated.

The invention includes compositions which comprise at least about 70wt.% of the substantially amorphous DMC complex catalysts of theinvention and up to about 30 wt. % of a highly crystalline DMC compound.More preferred compositions of the invention comprise at least about 90wt. % of the substantially amorphous DMC complex catalyst and up toabout 10 wt. % of the highly crystalline DMC compound. Most preferredare compositions that contain at least about 99 wt. % of thesubstantially amorphous DMC complex catalyst and up to about 1 wt. % ofthe highly crystalline material.

The catalyst compositions of the invention have relatively low surfaceareas. Conventional DMC compounds have surface areas within the range ofabout 50 to about 200 m² /g. In contrast, the surface areas of thecatalysts of the invention are preferably less than about 30 m² /g. Morepreferred compositions have surface areas less than about 20 m² /g.

Double metal cyanide compounds useful in the invention are the reactionproducts of a water-soluble metal salt and a water-soluble metal cyanidesalt. The water-soluble metal salt preferably has the general formulaM(X)_(n) in which M is selected from the group consisting of Zn(II),Fe(II), Ni(II), Mn(II), Co(II), Sn(II), Pb(II), Fe(III), Mo(IV), Mo(VI),Al(III), V(V), V(IV), Sr(II), W(IV), W(VI), Cu(II), and Cr(III). Morepreferably, M is selected from the group consisting of Zn(II), Fe(II),Co(II), and Ni(II). In the formula, X is preferably an anion selectedfrom the group consisting of halide, hydroxide, sulfate, carbonate,cyanide, oxalate, thiocyanate, isocyanate, isothiocyanate, carboxylate,and nitrate. The value of n is from 1 to 3 and satisfies the valencystate of M. Examples of suitable metal salts include, but are notlimited to, zinc chloride, zinc bromide, zinc acetate, zincacetonylacetate, zinc benzoate, zinc nitrate, iron(II) sulfate, iron(II)bromide, cobalt(II) chloride, cobalt(II) thiocyanate, nickel(II)formate, nickel(II) nitrate, and the like, and mixtures thereof.

The water-soluble metal cyanide salts used to make the double metalcyanide compounds useful in the invention preferably have the generalformula (Y)_(a) M'(CN)_(b) (A)_(c) in which M' is selected from thegroup consisting of Fe(II), Fe(III), Co(II), Co(III), Cr(II), Cr(III),Mn(II), Mn(III), Ir(III), Ni(II), Rh(III), Ru(II), V(IV), and V(V). Morepreferably, M' is selected from the group consisting of Co(II), Co(III),Fe(II), Fe(III), Cr(III), Ir(III), and Ni(II). The water-soluble metalcyanide salt can contain one or more of these metals. In the formula, Yis an alkali metal ion or alkaline earth metal ion. A is an anionselected from the group consisting of halide, hydroxide, sulfate,carbonate, cyanide, oxalate, thiocyanate, isocyanate, isothiocyanate,carboxylate, and nitrate. Both a and b are integers greater than orequal to 1; the sum of the charges of a, b, and c balances the charge ofM'. Suitable water-soluble metal cyanide salts include, but are notlimited to, potassium hexacyanocobaltate(III), potassiumhexacyanoferrate(II), potassium hexacyanoferrate(III), calciumhexacyanocobaltate(III), lithium hexacyanoiridate(III), and the like.

Examples of double metal cyanide compounds that can be used in theinvention include, for example, zinc hexacyanocobaltate(III), zinchexacyanoferrate(III), zinc hexacyanoferrate(II), nickel(II)hexacyanoferrate(II), cobalt(II) hexacyanocobaltate(III), and the like.Further examples of suitable double metal cyanide compounds are listedin U.S. Pat. No. 5,158,922, the teachings of which are incorporatedherein by reference.

The catalyst compositions of the invention are prepared in the presenceof a complexing agent. Generally, the complexing agent must berelatively soluble in water. Suitable complexing agents are thosecommonly known in the art, as taught, for example, in U.S. Pat. No.5,158,922. The complexing agent is added either during preparation orimmediately following precipitation of the catalyst. Usually, an excessamount of the complexing agent is used. Preferred complexing agents arewater-soluble heteroatom-containing organic compounds that can complexwith the double metal cyanide compound. Suitable complexing agentsinclude, but are not limited to, alcohols: aldehydes, ketones, ethers,esters, amides, ureas, nitriles, sulfides, and mixtures thereof.Preferred complexing agents are water-soluble aliphatic alcoholsselected from the group consisting of ethanol, isopropyl alcohol,n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, and tert-butylalcohol.

The conventional method of preparing DMC compounds useful for epoxidepolymerization is fully described in many references, including U.S.Pat. Nos. 5,158,922, 4,843,054, 4,477,589, 3,427,335, 3,427,334,3,427,256, 3,278,457, and 3,941,849, and Japanese Pat. Appl. Kokai No.4-145123. The teachings of these references related to conventionalcatalyst preparation and suitable DMC compounds are incorporated hereinby reference in their entirety.

The invention includes a method of making the substantially amorphousDMC catalyst compositions of the invention. The method comprises twosteps. First, aqueous solutions of a water-soluble metal salt and awater-soluble metal cyanide salt are intimately combined and reacted inthe presence of a complexing agent to produce an aqueous mixture thatcontains a precipitated DMC complex catalyst. Second, the catalyst isisolated and dried. The complexing agent can be included with either orboth of the aqueous salt solutions, or it can be added to the DMCcompound immediately following precipitation of the catalyst. It ispreferred to pre-mix the complexing agent with either the water-solublemetal cyanide salt, or with the water-soluble metal salt, or both,before intimately combining the reactants. The resulting catalystcomposition is substantially amorphous, as is evidenced by thesubstantial absence of highly crystalline DMC compound by X-raydiffraction analysis.

I have surprisingly discovered that achieving an intimate combination ofthe reactants is essential to preparing catalysts having lowcrystallinity. In conventional methods, the water-soluble metal salt andthe water-soluble metal cyanide salt are combined in aqueous media andare simply mixed together, typically with magnetic or mechanicalstirring. This method of preparation results in catalysts having asubstantial amount of highly crystalline DMC component, typicallygreater than about 35 wt. %. I have found that combining the reactantsin a manner effective to achieve an intimate combination of thereactants results in substantially amorphous catalysts that areexceptionally useful for epoxide polymerization. Suitable methods ofachieving this intimate combination of reactants include homogenization,impingement mixing, high-shear stirring, and the like. When thereactants are homogenized, for example, the level of crystallinematerial in the catalyst composition is minimized or eliminated, and ismuch lower than the amount of crystalline material present in a catalystmade by simple mixing.

The invention includes a process for making an epoxide polymer. Thisprocess comprises polymerizing an epoxide in the presence of a doublemetal cyanide catalyst composition of the invention. Preferred epoxidesare ethylene oxide, propylene oxide, butene oxides, styrene oxide, andthe like, and mixtures thereof. The process can be used to make randomor block copolymers. The epoxide polymer can be, for example, apolyether polyol derived from the polymerization of an epoxide in thepresence of a hydroxyl group-containing initiator.

Other monomers that will copolymerize with an epoxide in the presence ofa DMC compound can be included in the process of the invention to makeother types of epoxide polymers. Any of the copolymers known in the artmade using conventional DMC catalysts can be made with the catalysts ofthe invention. For example, epoxides copolymerize with oxetanes (astaught in U.S. Pat. Nos. 3,278,457 and 3,404,109) to give polyethers, orwith anhydrides (as taught in U.S. Pat. Nos. 5,145,883 and 3,538,043) togive polyester or polyetherester polyols. The preparation of polyether,polyester, and polyetherester polyols using double metal cyanidecatalysts is fully described, for example, in U.S. Pat. Nos. 5,223,583,5,145,883, 4,472,560, 3,941,849, 3,900,518, 3,538,043, 3,404,109,3,278,458, 3,278,457, and in J. L. Schuchardt and S. D. Harper, SPIProceedings, 32nd Annual Polyurethane Tech./Market. Conf. (1989) 360.The teachings of these references related to polyol synthesis using DMCcatalysts are incorporated herein by reference in their entirety.

The amorphous DMC catalysts of the invention are highly active comparedto conventional DMC catalysts (see Table 2). For example, a zinchexacyanocobaltate catalyst made using tert-butyl alcohol as acomplexing agent and made by homogenization (and containing less than 1wt. % of crystalline DMC compound by X-ray analysis) is about 65% moreactive at 100 ppm, and 200% more active at 130-250 ppm, than the samecatalyst made by simple mixing (and containing about 35 wt. %crystalline DMC compound). A consequence of higher polymerization ratesis that polyol producers can use less of the relatively expensive DMCcatalyst and save money. More active catalysts also permit the producerto reduce batch times and increase productivity.

The amorphous catalyst compositions of the invention show a reducedinduction period compared with conventional catalysts in a polyetherpolyol synthesis (see Table 3). Conventional DMC catalysts are notimmediately active toward epoxide polymerization. Typically, a starterpolyol, the catalyst, and a small amount of epoxide are combined andheated to the desired reaction temperature, and no epoxide polymerizesimmediately. The polyol manufacturer must wait (often for several hours)until the catalyst becomes active and the charged epoxide begins toreact before additional epoxide can safely be continuously added to thepolymerization reactor. The substantially amorphous catalysts of theinvention are more rapidly activated than conventional catalysts thatcontain up to 35 wt. % of crystalline DMC compound. This feature of thecatalysts is also an economic advantage because delays in adding theepoxide are reduced.

Polyether polyols prepared using the catalysts of the invention haveexceptionally low unsaturations, consistently less than about 0.007meq/g. These unsaturations are at least about 50% lower than polyolunsaturations available from the DMC catalysts previously known (seeTable 4). Preferred polyols of the invention have unsaturations lessthan about 0.006 meq/g, and more preferably less than about 0.005 meq/g.The reduction in unsaturation compared with polyols previously availablefrom conventional DMC catalysts should offer some advantages forpolyurethanes made with the polyols of the invention.

Polyether polyols made with the catalysts of the invention preferablyhave average hydroxyl functionalities from about 2 to 8, more preferablyfrom about 2 to 6, and most preferably from about 2 to 3. The polyolspreferably have number average molecular weights within the range ofabout 500 to about 50,000. A more preferred range is from about 1,000 toabout 12,000; most preferred is the range from about 2,000 to about8,000.

Polyols prepared with the catalysts of the invention also havesubstantially lower levels of low molecular weight polyol impuritiescompared with polyols prepared with conventional catalysts. Gelpermeation chromatography (GPC) analysis of these polyols shows nodetectable low molecular weight polyol impurities. In contrast,conventional DMC catalysts made in the usual way with glyme as acomplexing agent show a marked GPC peak corresponding to about 5-10 wt.% of a low molecular weight polyol impurity.

Interestingly, polyols made with the catalysts of the invention areusually clearer than polyols made with conventional glyme catalysts; theformer typically remain clear even after weeks of storage at roomtemperature, while the latter tend to quickly develop a haze duringstorage.

Another advantage of the substantially amorphous catalysts of theinvention is that they are more easily removed from polyether polyolsfollowing polyol synthesis compared with conventional DMC compounds. Theproblem of how to remove DMC compounds from polyether polyols has beenthe subject of many investigations (see, for example, U.S. Pat. Nos.5,144,093, 5,099,075, 5,010,047, 4,987,271, 4,877,906, 4,721,818, and4,355,188). Most of these methods irreversibly deactivate the catalyst.

The catalysts of the invention can be isolated by simply filtering thepolyol. Another way to isolate the catalyst is to first dilute thepolyol with a solvent such as heptane to reduce viscosity, then filterthe mixture to recover the catalyst, and then strip the polyol/heptanemixture to obtain the purified polyol. The methods described in U.S.Pat. No. 5,010,047 can also be used to recover the catalysts of theinvention from polyols. An advantage of the catalysts of the inventionis that they can be removed cleanly from polyols even with a hotfiltration in the absence of any solvent. In contrast, when a polyolmade with a conventional glyme catalyst is hot-filtered, substantialamounts of the DMC compound remain in the polyol. If desired, theisolated catalyst composition of the invention can be recovered andreused to catalyze another epoxide polymerization reaction because thesesimple filtration methods do not generally deactivate the catalysts.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

PREPARATION OF ZINC HEXACYANOCOBALTATE CATALYSTS BY HOMOGENIZATIONEXAMPLE 1 Tert-butyl Alcohol as the Complexing Agent (Catalyst D)

Potassium hexacyanocobaltate (8.0 g) is added to deionized water (150mL) in a beaker, and the mixture is blended with a homogenizer until thesolids dissolve. In a second beaker, zinc chloride (20 g) is dissolvedin deionized water (30 mL). The aqueous zinc chloride solution iscombined with the solution of the cobalt salt using a homogenizer tointimately mix the solutions. Immediately after combining the solutions,a mixture of tert-butyl alcohol (100 mL) and deionized water (100 mL) isadded slowly to the suspension of zinc hexacyanocobaltate, and themixture is homogenized for 10 min. The solids are isolated bycentrifugation, and are then homogenized for 10 min. with 250 mL of a70/30 (v:v) mixture of tert-butyl alcohol and deionized water. Thesolids are again isolated by centrifugation, and are finally homogenizedfor 10 min with 250 mL of tert-butyl alcohol. The catalyst is isolatedby centrifugation, and is dried in a vacuum oven at 50° C. and 30 in.(Hg) to constant weight. This catalyst is identified as Catalyst D.

PREPARATION OF ZINC HEXACYANOBALTATE CATALYSTS BY HOMOGENIZATION EXAMPLE2 Isopropyl Alcohol as the Complexing Agent (Catalyst E)

The procedure of Example 1 is modified as follows. Isopropyl alcohol issubstituted for tert-butyl alcohol. Following combination of the zincchloride and potassium hexacyanocobaltate solutions and homogenizationin the presence of isopropyl alcohol, the catalyst slurry is filteredthrough a 0.45 micron filter at 20 psi. The washing steps of Example 1are also repeated, but filtration rather than centrifugation is used toisolate the catalyst. The washed catalyst is dried to constant weight asdescribed above. The catalyst is identified as Catalyst E.

PREPARATION OF ZINC HEXACYANOCABALTATE CATALYSTS BY SIMPLE MIXINGCOMPARATIVE EXAMPLE 3 Tert-butyl Alcohol as the Complexing Agent(Catalyst B)

The procedure of Japanese Pat. Appl. Kokai No. 4-145123 is generallyfollowed. Potassium hexacyanocobaltate (4.0 g) is added to deionizedwater (75 mL) in a beaker, and the mixture is stirred until the solidsdissolve. In a second beaker, zinc chloride (10 g) is dissolved indeionized water (15 mL). The aqueous zinc chloride solution is combinedwith the solution of the cobalt salt using a magnetic stirring bar tomix the solutions. Immediately after combining the solutions, a mixtureof tert-butyl alcohol (50 mL) and deionized water (50 mL) is addedslowly to the suspension of zinc hexacyanocobaltate, and the mixture isstirred for 10 min. The solids are isolated by centrifugation, and arethen stirred for 10 min. with 100 mL of a 70/30 (v:v) mixture oftert-butyl alcohol and deionized water. The solids are again isolated bycentrifugation, and are finally stirred for 10 min with 100 mL oftert-butyl alcohol. The catalyst is isolated by centrifugation, and isdried in a vacuum oven at 50° C. and 30 in. (Hg) to constant weight.This catalyst is identified as Catalyst B.

PREPARATION OF ZINC HEXACYANOCOBALTATE CATALYSTS BY SIMPLE MIXINGCOMPARATIVE EXAMPLE 4 Isopropyl Alcohol as the Complexing Agent(Catalyst C)

The procedure of Comparative Example 3 is followed, except thatisopropyl alcohol is used in place of tert-butyl alcohol, and the solidsare isolated by filtration using a 0.8 micron filter rather than bycentrifugation. The catalyst is isolated and dried as described above.This catalyst is identified as Catalyst C.

COMPARATIVE EXAMPLE 5 PREPARATION OF CRYSTALLINE ZINC HEXACYANOCOBALTATENo Complexing Agent (Catalyst A)

Potassium hexacyanocobaltate (4.0 g) is dissolved in deionized water(150 mL) in a beaker. Zinc chloride (10 g) is dissolved in deionizedwater (15 mL) in a second beaker. The aqueous solutions are quicklycombined and magnetically stirred for 10 min. The precipitated solidsare isolated by centrifugation. The solids are reslurried in deionizedwater (100 mL) for 10 min. with stirring, and are again recovered bycentrifugation. The catalyst is dried in a vacuum oven at 50° C. and 30in. (Hg) to constant weight. This catalyst is identified as Catalyst A.

EXAMPLE 6 EPOXIDE POLYMERIZATIONS: RATE EXPERIMENTS--GENERAL PROCEDURE

A one-liter stirred reactor is charged with polyoxypropylene triol (700mol. wt.) starter (70 g) and zinc hexacyanocobaltate catalyst (0.057 to0.143 g, 100-250 ppm level in finished polyol, see Table 2). The mixtureis stirred and heated to 105° C., and is stripped under vacuum to removetraces of water from the triol starter. The reactor is pressurized toabout 1 psi with nitrogen. Propylene oxide (10-11 g) is added to thereactor in one portion, and the reactor pressure is monitored carefully.Additional propylene oxide is not added until an accelerated pressuredrop occurs in the reactor; the pressure drop is evidence that thecatalyst has become activated. When catalyst activation is verified, theremaining propylene oxide (490 g) is added gradually over about 1-3 h ata constant pressure of 20-24 psi. After propylene oxide addition iscomplete, the mixture is held at 105° C. until a constant pressure isobserved. Residual unreacted monomer is then stripped under vacuum fromthe polyol product, and the polyol is cooled and recovered.

To determine reaction rate, a plot of PO consumption (g) vs. reactiontime (min) is prepared (see FIG. 1). The slope of the curve at itssteepest point is measured to find the reaction rate in grams of POconverted per minute. The intersection of this line and a horizontalline extended from the baseline of the curve is taken as the inductiontime (in minutes) required for the catalyst to become active. Theresults of reaction rates and induction times measured for variouscatalysts at 100-250 ppm catalyst levels appear in Tables 2 and 3.

EXAMPLE 7 POLYETHER POLYOL SYNTHESIS: EFFECT OF CATALYST ON POLYOLUNSATURATION, CATALYST REMOVAL, AND POLYOL QUALITY

A two-gallon stirred reactor is charged with polyoxypropylene triol (700mol. wt.) starter (685 g) and zinc hexacyanocobaltate catalyst (1.63 g).The mixture is stirred and heated to 105° C., and is stripped undervacuum to remove traces of water from the triol starter. Propylene oxide(102 g) is fed to the reactor, initially under a vacuum of 30 in. (Hg),and the reactor pressure is monitored carefully. Additional propyleneoxide is not added until an accelerated pressure drop occurs in thereactor; the pressure drop is evidence that the catalyst has becomeactivated. When catalyst activation is verified, the remaining propyleneoxide (5713 g) is added gradually over about 2 h while maintaining areactor pressure less than 40 psi. After propylene oxide addition iscomplete, the mixture is held at 105° C. until a constant pressure isobserved. Residual unreacted monomer is then stripped under vacuum fromthe polyol product. The hot polyol product is filtered at 100° C.through a filter cartridge (0.45 to 1.2 microns) attached to the bottomof the reactor to remove the catalyst. Residual Zn and Co are quantifiedby X-ray analysis.

Polyether diols (from polypropylene glycol starter, 450 mol. wt.) andtriols are prepared as described above using zinc hexacyanocobaltatecatalysts made by conventional methods (stirring) and by the method ofthe invention (homogenization). The impact of the catalysts of theinvention on epoxide polymerization rate (Table 2), induction period(Table 3), polyol unsaturation (Table 4), catalyst removal (Table 5),and polyol quality (Table 6) are shown in the tables.

The preceding examples are meant only as illustrations. The scope of theinvention is defined by the claims.

                                      TABLE 1                                     __________________________________________________________________________    DMC Catalyst Characterization                                                          X-Ray Diffraction Pattern                                                     (d-spacings, angstroms).sup.1                                                                         Surface area                                 ID Catalyst                                                                            5.07                                                                              4.82                                                                              3.76                                                                              3.59                                                                              2.54                                                                              2.28                                                                              (m.sup.2 /g)                                 __________________________________________________________________________    A  Cryst.                                                                              X   absent                                                                            absent                                                                            X   X   X   454                                             Zn--Co.sup.2                                                               B  TBA   X   X   X   X   X   X   82                                              stirred.sup.2                                                              C  IPA   X   absent                                                                            X   X   X   X   n.m.                                            stirred.sup.2                                                              D  TBA   absent                                                                            X   X   absent                                                                            absent                                                                            absent                                                                            14                                              homog..sup.3                                                               E  IPA   absent                                                                            X   X   absent                                                                            absent                                                                            absent                                                                            n.m.                                            homog..sup.3                                                               __________________________________________________________________________     X = Xray diffraction line present;                                            n.m. = not measured.                                                          Samples were analyzed by Xray diffraction using monochromatized               CuKα.sub.1 radiation (λ = 1.54059 Å). A Seimens D500         Kristalloflex diffractometer powered at 40 kV and 30 mA was operated in a     step scan mode of 0.02° 2θ with a counting time of 2             seconds/step. Divergence slits of 1° in conjunction with               monochrometer and detector apertures of 0.05° and 0.15°         respectively. Each sample was run from 5° to 70° 2θ.      .sup.1 Water of hydration can cause minor variations in measured              dspacings.                                                                    .sup.2 Comparative example.                                                   .sup.3 Catalyst of the invention.                                        

                  TABLE 2                                                         ______________________________________                                        Effect of Catalyst on Epoxide Polymerization Rate (105° C.)            ID  Catalyst   Cat. amt. (ppm)                                                                           Rate of polymerization (g/min)                     ______________________________________                                        F   glyme.sup.1,2                                                                            250         3.50                                                              130         1.78                                                              100         1.46                                               B   TBA stirred.sup.2                                                                        250         3.64                                                              130         2.50                                                              100         2.29                                               D   TBA homog..sup.3                                                                         250         10.5                                                              130         7.40                                                              100         3.84                                               C   IPA stirred.sup.2                                                                        250         <0.3                                               E   IPA homog..sup.3                                                                         250         1.70                                               ______________________________________                                         .sup.1 Catalyst F is prepared as described in U.S. Pat. No. 5,158,922.        .sup.2 Comparative example.                                                   .sup.3 Catalyst of the invention.                                        

                  TABLE 3                                                         ______________________________________                                        Effect of Catalyst on Induction Period (105° C.)                                         Catalyst                                                                      concentration                                               ID     Catalyst   (ppm)      Induction Time (min)                             ______________________________________                                        F      glyme.sup.1,2                                                                            100        230                                                                250        180                                              B      TBA stirred.sup.2                                                                        100        220                                                                130        180                                                                250         90                                              D      TBA homog..sup.3                                                                         100        140                                                                130        130                                                                250         85                                              ______________________________________                                         .sup.1 Catalyst F is prepared as described in U.S. Pat. No. 5,158,922.        .sup.2 Comparative example.                                                   .sup.3 Catalyst of the invention.                                        

                  TABLE 4                                                         ______________________________________                                        Effect of Catalyst on Polyol Unsaturation                                                     Polyol OH #        Polyol                                                     (mg KOH/g)         unsaturation                               ID   Catalyst   and functionality                                                                          Solvent                                                                             (meq/g)                                    ______________________________________                                        F    glyme.sup.1,2                                                                            54 (Triol)   none  0.016                                                      27 (Triol)   none  0.017                                                      15 (Triol)   none  0.019                                      B    TBA stirred.sup.2                                                                        35 (Triol)   none  0.011                                                      27 (Triol)   none  0.010                                                      14 (Triol)   none  0.011                                      D    TBA homog..sup.3                                                                         27 (Triol)   none  0.005                                                      56 (Diol)    none  0.004                                                      27 (Diol)    none  0.005                                                      14 (Diol)    none  0.004                                                      31 (Triol)   THF   0.003                                                      12 (Triol)   heptane                                                                             0.006                                      ______________________________________                                         .sup.1 Catalyst F is prepared as described in U.S. Pat. No. 5,158,922.        .sup.2 Comparative example.                                                   .sup.3 Catalyst of the invention.                                        

                  TABLE 5                                                         ______________________________________                                        Effect of Catalyst on Catalyst Removal                                                                           Residual                                           Polyol OH #                                                                             Filtration       catalyst                                           (mg KOH/g)                                                                              Temp.            (ppm)                                      ID   Catalyst and functionality                                                                         (°C.)                                                                         Solvent                                                                             Zn   Co                                ______________________________________                                        F    glyme.sup.1,2                                                                          27 (Triol)  100    none  28   12                                B    TBA      25 (Triol)  100    none  6    3                                      stirred.sup.2                                                            D    TBA      25 (Triol)  100    none  5    <2                                     homog..sup.3                                                                           14 (Diol).sup.                                                                            100    none  4    <2                                              29 (Diol).sup.                                                                            100    none  3    <2                                              14 (Triol)  100    none  4    <2                                              27 (Triol)   25    heptane                                                                             3    <2                                              14 (Diol).sup.                                                                             25    heptane                                                                             6    <2                                ______________________________________                                         .sup.1 Catalyst F is prepared as described in U.S. Pat. No. 5,158,922.        .sup.2 Comparative example.                                                   .sup.3 Catalyst of the invention.                                        

                  TABLE 6                                                         ______________________________________                                        Effect of Catalyst on Polyol Purity and Clarity                                            Low Mol. Wt.                                                                  Polyol Impurity                                                  ID   Catalyst                                                                              (Wt. %, by GPC)                                                                           Appearance (25° C., after 3                   ______________________________________                                                                 weeks)                                               F    glyme   5-10        hazy                                                 D    TBA     none detected                                                                             clear                                                ______________________________________                                    

I claim:
 1. A method which comprises:(a) heating an epoxide and,optionally, a starter polyol, in the presence of a catalyst whichcomprises at least about 70 wt. % of a substantially amorphous doublemetal cyanide complex under conditions effective to polymerize theepoxide and produce a polyether polyol; and (b) filtering the polyetherpolyol, optionally in the presence of a solvent, to remove the doublemetal cyanide complex from the polyether polyol.
 2. The method of claim1 wherein the catalyst further comprises up to about 30 wt. % of acrystalline double metal cyanide compound.
 3. A method whichcomprises:(a) heating an epoxide and, optionally, a starter polyol, inthe presence of a double metal cyanide complex catalyst that exhibits apowder X-ray diffraction pattern having no sharp lines at about 5.1(d-spacing, angstroms) under conditions effective to polymerize theepoxide and produce a polyether polyol; and (b) filtering the polyetherpolyol, optionally in the presence of a solvent, to remove the doublemetal cyanide complex from the polyether polyol.